Combustible fuel burning stove with fire grate

ABSTRACT

Disclosed is a stove that includes a dome-shaped fire grate comprising a center, a perimeter surrounding and spaced from the center, the center being higher than the perimeter; a plurality of radial stiffening ribs extending away from the perimeter and toward the center; at least one circumferential stiffening ring extending at least partially about the center; and a plurality of ventilation holes between the center and the perimeter.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 16/366,799 filed Mar. 27, 2019, entitled “Combustible FuelBurning Stove with Fire Grate,” which is hereby incorporated byreference in its entirety for all purposes.

TECHNICAL FIELD

The subject matter described herein relates to a combustible fuelburning stove with a fire grate. This fire grate has particular but notexclusive utility for portable back yard firepits.

BACKGROUND

Portable wood burning stoves are used in camping and make use of twigsand sticks as fuel for heat and cooking. Similarly, large portablefirepits are used for example in residential back yards for recreation,to provide outdoor heat, and to support limited cooking such asmarshmallow roasting.

However, large firepits are generally fueled by piles of heavy logsrather than small twigs, which places significantly greater structuraldemands on the firepit materials. When experiencing repeated cycles ofcold (during disuse) and high heat (during use), fire grates for largefirepits are subject to bowing or sagging that may be aestheticallydispleasing, may cause a poor fit with other components of the firepit,and may cause unwanted contact with other components of the firepit, orwith the ground, thus presenting a potential fire risk. Large firegrates are also subject to oxidation, and to other deformation that maylimit their service life and may, in some circumstances, cause dangerousstructural failure with additional attendant fire risk. Conventionalfire grates are subject to deformation or may have insufficient airflow, which in turn may lead to inadequate combustion of fuel,inadequate heat production, and excessive generation of smoke. Suchheavily built structures are also heavier (and therefore less portable),they require more material to construct, and they may also require morecomplex (and therefore more expensive) manufacturing steps.

It is therefore to be appreciated that such commonly used fire grateshave numerous drawbacks, including one or more of high cost, largeweight, low portability, poor performance, short service life, smokegeneration, fire risk, aesthetic degradation, among others. Accordingly,long-felt needs exist for fire grates that address the forgoing andother concerns.

The information included in this Background section of thespecification, including any references cited herein and any descriptionor discussion thereof, is included for technical reference purposes onlyand is not to be regarded as subject matter by which the scope of thedisclosure is to be bound.

SUMMARY

Disclosed is a fire grate for a wood burning stove. One general aspectincludes a stove including: a dome-shaped fire grate including: acenter; a perimeter surrounding and spaced from the center, the centerbeing higher than the perimeter; a plurality of radial stiffening ribsextending away from the perimeter and toward the center; at least onecircumferential stiffening ring extending at least partially about thecenter; and a plurality of ventilation holes between the center and theperimeter.

Implementations may include one or more of the following features. Thestove where the perimeter is circular. The stove where the dome-shapedfire grate is a spherical section with a radius of curvature larger thanone-half of a width of the fire grate. The stove where the centerincludes a central hub. The stove where the fire grate further includesa downward-facing lip around the perimeter. The stove where theplurality of radial stiffening ribs include ribs of at least twodifferent lengths. The stove where a portion of the dome-shaped firegrate includes an outer stiffening ring that includes no ventilationholes. The stove where the dome-shaped fire grate, the plurality ofradial stiffening ribs, the at least one circumferential stiffeningring, and the ventilation holes are arranged in a manner that they canbe produced by stamping a flat blank of metallic material. The stoveincluding: an outer wall, an inner wall spaced from the outer wall by agap, the inner wall forming a cavity, and where the dome-shaped firegrate is disposed in the cavity. The stove where the ventilation holesare in fluid communication with the gap in a manner assisting with airflow through the gap, and where the fire grate is configured to supportbetween 0 lb and about 190 lb of fuel at temperatures of between about−40 f and about 1350 f.

One general aspect includes a fire grate for a combustion stove,including: a domed shape having a center and a perimeter, where thecenter is higher than the perimeter; a plurality of radial stiffeningribs extending away from the perimeter and toward the center; at leastone circumferential stiffening ring extending at least partially aboutthe center; and a plurality of ventilation holes between the center andthe perimeter.

Implementations may include one or more of the following features. Thefire grate where the perimeter is circular. The fire grate where thedomed shape is a spherical section with a radius of curvature largerthan one-half of a width of the fire grate. The fire grate including acentral hub. The fire grate including a downward-facing lip around theperimeter. The fire grate where the plurality of radial stiffening ribsextend from the perimeter, and include radial stiffening ribs of atleast two different lengths. The fire grate where a portion of the domedshape includes an outer stiffening ring that includes no ventilationholes. The fire grate where the shape of the fire grate is configured toenable production by stamping a flat blank of metallic material.

One general aspect includes a stove for burning solid fuel to produceheat, including: an inner wall having a lower portion and an upperportion; an outer wall having a lower portion and an upper portion; anair-filled space between the inner and outer wall; a chimney formed bythe inner wall; a combustion area situated within the chimney; at leastone ventilation hole within the upper portion of the inner wall; atleast one ventilation hole within the lower portion of the outer wall; afire grate situated within the combustion area, including: a domed shapehaving a center and a perimeter, where the center is higher than theperimeter; a plurality of radial stiffening ribs substantially orientedtoward the center; at least one circumferential stiffening ringssubstantially concentric with the center; a stiffening lip around theperimeter; and a plurality of ventilation holes. Implementations mayinclude the stove where the fire grate is supported only at theperimeter.

The fire grate disclosed herein has particular, but not exclusive,utility for portable back yard firepits.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tolimit the scope of the claimed subject matter. A more extensivepresentation of features, details, utilities, and advantages of the firegrate, as defined in the claims, is provided in the following writtendescription of various embodiments of the disclosure and illustrated inthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the present disclosure will be describedwith reference to the accompanying drawings, of which:

FIG. 1 is a cross sectional view of an example wood burning stove with afire grate in accordance with at least one embodiment of the presentdisclosure.

FIG. 2 is an exemplary representation of a fire grate for a wood burningstove in accordance with at least one embodiment of the presentdisclosure.

FIG. 3 is an exemplary representation of a fire grate for a wood burningstove in accordance with at least one embodiment of the presentdisclosure.

FIG. 4 is an exemplary representation of a fire grate for a wood burningstove in accordance with at least one embodiment of the presentdisclosure.

FIG. 5 is an exemplary representation of a fire grate for a wood burningstove in accordance with at least one embodiment of the presentdisclosure.

FIG. 6 is a cross-sectional view of an example stiffening rib orstiffening ring of an example fire grate for a wood burning stove inaccordance with at least one embodiment of the present disclosure.

FIG. 7 is an exemplary representation of a fire grate 100 for a woodburning stove 150 in accordance with at least one embodiment of thepresent disclosure.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thepresent disclosure, reference will now be made to the embodimentsillustrated in the drawings, and specific language will be used todescribe the same. It is nevertheless understood that no limitation tothe scope of the disclosure is intended. Any alterations and furthermodifications to the described devices, systems, and methods, and anyfurther application of the principles of the present disclosure arefully contemplated and included within the present disclosure as wouldnormally occur to one skilled in the art to which the disclosurerelates. In particular, it is fully contemplated that the features,components, and/or steps described with respect to one embodiment may becombined with the features, components, and/or steps described withrespect to other embodiments of the present disclosure. For the sake ofbrevity, however, the numerous iterations of these combinations will notbe described separately.

In accordance with at least one embodiment of the present disclosure, afire grate for a wood burning stove is provided which includes novelstructural features to prevent significant bending, bowing, sagging, orother deformation under the heat loads expected during normal use casesand plausible exceptional use cases. These features provide thenecessary structural performance to support heavy fuel loads at hightemperature, while permitting a relatively low weight for the fire grateitself. The disclosed fire grate also includes air flow featuresconducive to thorough combustion of fuel, which leads to greater heatgeneration and substantially reduced smoke. The design may be readilymanufactured as a single piece (e.g., stamped from a sheet metal blank),which permits it to be lighter and less expensive than a multipartassembly of comparable strength.

These descriptions are provided for exemplary purposes only and shouldnot be considered to limit the scope of the fire grate. Certain featuresmay be added, removed, or modified without departing from the spirit ofthe claimed subject matter.

FIG. 1 is a cross-sectional view of an example combustion stove, such asa wood burning stove 150 including a fire grate 100 in accordance withat least one embodiment of the present disclosure. The fire grate 100sits within the stove or fire pit 150 and supports the weight of fuel160 (e.g., wooden logs and sticks) while permitting air flow through thefire grate 100 and stove or fire pit 150 to facilitate combustion of thefuel 160. The fire grate 100 is strong and stiff to bear the weight offirewood and other fuel 160, both at ambient temperatures and atoperating temperatures, and may resist substantial warping or othersubstantial deformation despite prolonged and repeated exposure to theheat of combustion. The fire grate 100 may also be lighter and havegreater airflow than other fire grates of comparable size.

In the example embodiment of FIG. 1, the combustion stove 150 includes atop portion 152, a bottom portion 154, and a middle portion 156. Thefirepit 150 further includes an inner wall or inner body 110, an outerwall or outer body 120, a connecting ring 125 located in the top portion152 of the stove 150 and attached to or formed as a single piece withthe inner body 110 and the outer body 120, and a cavity 190 defined bythe inner body 110, within which the fire grate 100 is positioned. Thestove 150 further includes a top lip 115 attached to or formed as asingle piece with either of the inner body 110 and outer body 120. Thestove 150 further includes a plurality of outer ventilation holes 122located in the bottom portion 154 of the outer body 120, and a pluralityof inner ventilation holes 124 located in the top portion 152 of theinner body 110. In the middle portion 156 of the stove 150, the innerbody 110 terminates in an upward-facing support lip or rollover 112 intowhich the fire grate 100 fits, or upon which the fire grate 100 rests.

The stove 150 further includes a base plate 170 attached to the outerbody 120, a bracing tray 175 supported by stands projecting upward fromthe base plate, and a catch tray 180 supported by stands projectingupward from the bracing tray 175 such that the bracing tray is separatedfrom the outer body by an air gap 176, the catch tray 180 is separatedfrom the outer body 120 by an air gap 178, and the inner body isseparated from the outer body by an air gap 179. In an example, air gaps176 and 179 are both about 50 mm, while air gap 178 is about 100 mm,although other air gaps may be employed that have the disclosed,advantageous effect.

The cavity 190 is in fluid communication with the air gap 179 via theinner ventilation holes 124, and with air gaps 178 and 176 via the firegrate 100. The air gaps 176 and 178 are in fluid communication withambient air via the outer ventilation holes 122, such that ambient airmay be drawn in through the outer ventilation holes 122, heated bycombustion of the fuel 160, and expelled through the cavity 190 andinner ventilation holes 124 to produce advantageous combustion of thefuel 160.

In an example, both the fire grate 100 and the stove or firepit 150 aremade of stainless steel plates having a thickness within a range ofbetween about 0.5 mm and about 2.5 mm thick. Some examples of the firegrate 100 and the stove or firepit 150 are formed of 1.0 mm to 2.0 mmthick, and one example is about 1.5 mm thick stainless steel. Boththicker and thinner materials are contemplated. In an example, the firegrate 100 weighs approximately 48 lb (21.8 kg), although weights ofbetween about 9 oz and about 88 lb may be provided. In an example,during normal operation the fire grate 100 supports a nominal weight of100 lb (45.4 kg), (although nominal capacities of between about 5 lb andabout 190 lb may be provided), while the fire grate 100, or portionsthereof, are heated to between about about 700° F. (371° C.) and about1350° F. (732° C.) by the combustion of the fuel 160, for a time periodof between 1 and 12 hours, and also at ambient temperatures as low as−40° F. (−40° C.)In an example, during normal operation over a period ofyears, with repeated cycling (e.g., one hundred cycles) between ambientand operational temperatures, the fire grate 100 exhibits little or nowarping that would detrimentally affect its aesthetic appearance, itsperformance, or its fit within the stove or firepit 150.

The primary load carried by the fire grate 100 is applied downward, in adirection parallel to axis 270, by the weight of the fuel 160 piled onthe fire grate 100, which is supported by the upward-facing lip orrollover 112 of the inner body 110.

FIG. 2 is an exemplary representation of a fire grate 100 for a woodburning stove in accordance with at least one embodiment of the presentdisclosure. In the example shown in the figure, the fire grate is acircular, convex, dome-shaped structure that includes an outer rim 310with a downward-facing lip or rollover 312 that provides stiffness, thatfits into the upward facing lip or rollover 112 of the inner body 110 ofthe stove or firepit 150, and makes it more difficult for the outer rim310 of the fire grate 100 to dent, warp, or otherwise deform. The outerrim 310 may define the axis 270. In this example, the fire grate 100further includes a central hub 320 that is raised above the outer rim310, a stiff outer ring 315, and a ventilated inner ring 325 thatreaches from the inner edge 318 of the stiff outer ring 315 to the outeredge 518 of the central hub 320 (see FIG. 5). The ventilated inner ring325 includes a plurality of ventilation holes 330.

In an example having an outer diameter 420 (see FIG. 4), the ventilatedinner ring 325 includes 504 circular ventilation holes, each with adiameter of about 10 mm Other numbers and sizes of holes could be used(e.g., 50-800 holes, each with a diameter of between 0.5 cm and 1.5 cm),although while more holes and/or larger holes would mean better overallventilation, it may mean less structural material and thus a weakerstructure for both the ventilated inner ring 325 and the fire grate 100overall. Because better ventilation may result in higher firetemperatures, the structure may weaken further due to a combination ofheat softening and heat expansion. A weaker structure may have a reducedability to support the weight of firewood or other fuel piled on top ofit (see FIG. 1), and may be more prone to collapse or warping.Conversely, fewer holes and/or smaller holes may result in a strongeroverall structure and better support for firewood or other fuel, it mayalso result in worse ventilation and thus a lower combustiontemperature, less head output, and increased generation of smoke.

In the implementation in FIG. 2, the stiff outer ring 315 includes aplurality of short radial stiffening ribs 340 that reach from the outerrim 310 to the outer edge 318 of the ventilated inner ring 325. In someexamples, the ventilated inner ring 325 of the fire grate 100 includestwenty-four short radial stiffening ribs 340, although other examplesmay include a different number of short radial stiffening ribs 340 solong as they achieve the advantageous effects. In an example, the shortradial stiffening ribs 340 reach a short distance (e.g., 5 mm) into theventilated inner ring, such that the ends 342 of the short radialstiffening ribs 340 may be at the same radial distance from the centerof the hub 320 as the centers of the outermost ventilation holes 330.Other lengths are possible for the short radial stiffening ribs 340,although shorter ribs 340 would provide less structural support andstiffening, and longer ribs 340 may displace, cover, or otherwiseinterfere with some of the ventilation holes 330.

The fire grate 100 in the example shown in FIG. 2 may further include aplurality of long radial stiffening ribs 350 and 355 that reach from theouter rim 310 to, or nearly to, the central hub 320. In the exampleshown in FIG. 2, six long stiffening ribs 350 reach all the way to thecentral hub 320, while six interleaved long stiffening ribs 355 approachbut do not reach with central hub 320. In some examples, the interleavedlong stiffening ribs 355 reach within about 5 mm of the hub. In someimplementations, the interleaved long stiffening ribs 355 extend all theway to the central hub 320. Such implementations however would result ina majority of the circumference of the central hub 320 comprisinginterfaces between ribs and the hub itself, which may result in a weakeroverall structure. In other implementations, the long stiffening ribs350 may be shortened such that they do not reach all the way to, or donot intersect the central hub 320. In some implementations, thestiffening ribs 355 may be shortened even further, so that theirdistance from the central hub 320 is in a range of about 5-50 mm, forexample. However, increasing the distance from the central hub 320 orintersecting the central hub 320 with the interleaved long stiffeningribs 355 may result in less stiffening and thus a weaker structureoverall. Depending on the implementation, other numbers of longstiffening ribs 350 and 355 could be used, although more long radialstiffening ribs 350 or 355 may mean fewer ventilation holes, and fewerlong radial stiffening ribs 350 or 355 may mean a weaker, less stiff,structure that is more prone to crushing and/or warping.

In addition to the plurality of ventilation holes 330, the ventilatedinner ring 325 includes an outer concentric stiffening ring 360 and aninner concentric stiffening ring 370 that provide additional strength,stiffness, and stability to the structure of the fire grate 100, both atambient temperature and at operating temperatures when a fire is burningin the fire pit 150 that includes the fire grate (see FIG. 1). In otherembodiments, the fire grate 100 could include more than two stiffeningrings. For example, some embodiments include between 3 and 5 stiffeningrings. Even greater numbers of stiffening rings are contemplated.However, increasing the number of stiffening rings may reduce the numberor size of the holes 330, with effects as described above, or elsedecrease the spacing between the holes 330, which may weaken thestructure of the fire grate 100. In still other embodiments, the firegrate 100 may include fewer than two stiffening rings, which may resultin a weaker, less stiff structure with more space available forventilation holes.

In the example shown in FIG. 2, the central hub 320 having a centralventilation hole 323. In other embodiments, the central hub 320 is notpresent or does not include a central hole 323.

In an example, the hub 320, short stiffening ribs 330, long stiffeningribs 350 and 355, stiffening rings 370 and 370 are stamped or otherwiseembossed into the material of the fire grate (e.g., stainless steel),although other fabrication methods may be employed. In an example, thefire grate is a spherical section which is formed from a flat, circularblank by the stamping process. In an example, the holes 330 and 323 arealso formed by the stamping process, although they may alternatively beproduced by drilling, laser cutting, or other methods.

In some embodiments, one or more of the holes 330 may overlap with oneor more of the stiffening ribs 340, 350, or 355, or stiffening rings 360and 370. However, in other embodiments the hole pattern, rib pattern,and ring pattern have been selected such that no holes 330 overlap withany of the ribs 340, 350, or 355, or rings 360 and 370.

FIG. 3 is an exemplary representation of a fire grate 100 for a woodburning stove in accordance with at least one embodiment of the presentdisclosure. The fire grate 100 has a diameter 410 and includes the innerventilated ring 325 with an outer diameter 420, the outer stiffeningring with a diameter 430, and the inner stiffening ring with a diameter440. In an example, diameter 410 is about 697 mm (although valuesbetween about 101 mm and about 1270 mm may be provided), diameter 420 isabout 577 mm (although values between about 83 mm and about 1050 mm maybe provided), diameter 430 is about 439 mm (although values betweenabout 63 mm and about 800 mm may be provided), and diameter 440 is about286 mm (although values between about 41 mm and about 520 mm may beprovided). Other diameters could be used, making the fire grate largeror smaller for different applications.

The fire grate 100 also includes the plurality of short radialstiffening ribs 340, each separated from its nearest neighboring shortradial stiffening rib 340 by an angle 470. The fire grate 100 includes aplurality of long radial stiffening ribs 355 interleaved with slightlylonger radial stiffening ribs 350. Each long radial stiffening rib 350or 355 is separated from its nearest neighboring long radial stiffeningrib 350 or 355 by an angle 450, and from its nearest neighboring shortradial stiffening rib by an angle 460. In an example, angle 450 is 30degrees, while angles 460 and 470 are both 10 degrees. However, otherangle spacing is contemplated.

The length of the short radial ribs 340 is roughly equal to one half thedifference between diameter 410 and diameter 420. In an example, thisnumber is equal to 60 mm, and the short radial ribs 340 are each aboutfive millimeters longer than that, although other lengths may beemployed. In an example, the length of the long radial stiffening ribs350 is about 322.5 mm, and the length of the long radial stiffening ribs355 is about 317.5 mm, although other lengths could be employed.

FIG. 4 is an exemplary representation of a fire grate 100 for a woodburning stove in accordance with at least one embodiment of the presentdisclosure. The fire grate 100 has a height 510 and a radius ofcurvature 420. The lip 312 has a height 530. In an example, height 510is about 103 mm (although heights of between about 10 mm and about 180mm may be provided, including for larger or smaller fire grates), radiusof curvature 420 is about 716 mm (although radii of between about 100 mmand about 1350 mm may be provided, including for larger or smaller firegrates), and height 530 is about 12.6 mm (although heights of betweenabout 2 mm and about 24 mm may be provided, including for larger orsmaller fire grates). Other heights and radii of curvature could beused, but may affect the strength, stiffness, heat softening, and heatexpansion properties of the fire grate 100.

FIG. 5 is an exemplary representation of a fire grate 100 for a woodburning stove 150 in accordance with at least one embodiment of thepresent disclosure. In the example shown in the figure, the hub 320 hasa diameter 510, the long radial stiffening ribs 350 and 355 have a width520, and the long radial stiffening ribs 355 have a separation 530 fromouter edge of the hub. In an example, diameter 510 is about 52 mm(although values between about 5 mm and about 100 mm may be provided),width 520 is about 10 mm (although values between about 5 mm and about20 mm may be provided), and separation 530 is about 5 mm (althoughvalues between 0 mm and about 300 mm may be provided in someimplementations). Still other values are contemplated that create thedisclosed, advantageous effect. In an example, the short radialstiffening ribs 340 have the same width as the long stiffening ribs 350and 355, although other widths could be employed that had the disclosedeffect.

FIG. 6 is cross-sectional representation of an example stiffening rib340, 350, or 355 or stiffening ring 360 or 370 of an example fire grate100 for a wood burning stove or firepit 150 in accordance with at leastone embodiment of the present disclosure. The fire grate 100 has amaterial thickness 610, which has been stamped or otherwise embossedwith a linear feature 620 (i.e., a stiffening rib or ring) representedhere in cross section. The linear feature 620 has an inner radius ofcurvature 630, an outer radius of curvature 640, and a height 650 abovethe surface of the fire grate 100. In an example, thickness 610 is about1.5 mm, inner radius 630 is about 2.5 mm, outer radius 640 is about 4mm, and height 650 is about 3 mm Other values could be employed that hadthe disclosed advantageous effects.

FIG. 7 is an exemplary representation of a fire grate 100 for a woodburning stove 150 in accordance with at least one embodiment of thepresent disclosure. The example of FIG. 7 shows a closer view of thedownward-facing lip or rollover 312, which is part of the outer rim 310of the fire grate 100. In an example the lip or rollover 312 has aheight 530 of about 12.6 mm and a thickness 610 of about 1.5 mm In someembodiments, the outer rim 310 of the fire grate 100 is circular. Inother embodiments, the outer rim 310 may be a regular polygon such as ahexagon, octagon, or approximately circular polygon with a plurality ofsides. In still other embodiments, the outer rim 310 may be oval shaped.

The fire grate 100 is made strong and stiff for load bearing of firewoodand other fuel, both at ambient temperatures and at operatingtemperatures, by a balanced combination of a domed shape, a verticallyfolded outer lip 312, stiff outer ring 315, short radial stiffening ribs340, long radial stiffening ribs 350 and 355, a central hub, andstiffening rings 360 and 370. At the same time, the fire grate 100 isventilated by a ventilated inner ring 325 that includes a plurality ofventilation holes 330, and by a single ventilation hole 323 at thecenter of the central hub 320. The ventilation provided by thesefeatures is sufficient to provide high air circulation through the stoveor firepit 150 to yield a high heat output and low smoke output relativeto existing stoves and firepits.

Accordingly, it can be seen that the fire grate 100 fills along-standing need in the art, by providing a low-cost, lightweight,stampable, high-strength, high-stiffness, high-airflow structure thatresists denting, warping, and other deformation while carrying heavyfuel loads at operating temperatures as high as about 1350° F. (732°C.), and while cycling repeatedly between ambient temperature andoperating temperature.

A number of variations are possible on the examples and embodimentsdescribed hereinabove. For example, the fire grate could be made ofheavier-gauge material in order to support more weight, or of lightergauge material in order to become lighter and more portable. The firegrate could be made in different sizes and/or with different degrees ofcurvature. The relative lengths, widths, and radii of differentcomponents could be different than presented herein. The fire gratecould be made by different processes, including casting, forging,sintering, milling, or 3D printing. It could be made of differentmetals, or of nonmetallic materials such as ceramics. The outer rimcould be noncircular, including such possible shapes as ovals,rectangles, triangles, and rhombuses. The technology described hereinmay be used to burn firewood, wood chips or pellets, scrap lumber,paper, cardboard, coal, and other combustible materials. It may beemployed for example in lamps, stoves, firepits, fireplaces, furnaces,forges, and boilers, and other combustion heaters. In someimplementations, more than one fire grate may be used, or the fire gratemay comprise several pieces that collectively form a structure like thatdescribed herein.

The logical operations making up the embodiments of the technologydescribed herein are referred to variously as operations, steps,objects, elements, components, or modules. Furthermore, it should beunderstood that these may be performed in any order, unless explicitlyclaimed otherwise or a specific order is inherently necessitated by theclaim language.

All directional references e.g., upper, lower, inner, outer, upward,downward, left, right, lateral, front, back, top, bottom, above, below,vertical, horizontal, clockwise, counterclockwise, proximal, and distalare only used for identification purposes to aid the reader'sunderstanding of the claimed subject matter, and do not createlimitations, particularly as to the position, orientation, or use of thefire grate. Connection references, e.g., attached, coupled, connected,and joined are to be construed broadly and may include intermediatemembers between a collection of elements and relative movement betweenelements unless otherwise indicated. As such, connection references donot necessarily imply that two elements are directly connected and infixed relation to each other. The term “or” shall be interpreted to mean“and/or” rather than “exclusive or.” Unless otherwise noted in theclaims, stated values shall be interpreted as illustrative only andshall not be taken to be limiting.

The above specification, examples and data provide a completedescription of the structure and use of exemplary embodiments of thefire grate as defined in the claims. Although various embodiments of theclaimed subject matter have been described above with a certain degreeof particularity, or with reference to one or more individualembodiments, those skilled in the art could make numerous alterations tothe disclosed embodiments without departing from the spirit or scope ofthe claimed subject matter. Still other embodiments are contemplated. Itis intended that all matter contained in the above description and shownin the accompanying drawings shall be interpreted as illustrative onlyof particular embodiments and not limiting. Changes in detail orstructure may be made without departing from the basic elements of thesubject matter as defined in the following claims.

1-20. (canceled)
 21. A fire pit comprising: an outer wall comprising aplurality of air ventilation holes; an inner wall spaced from the outerwall to form an air gap therebetween, the inner wall comprising aplurality of air ventilation holes, the inner wall defining a cavity andhaving a central axis; a fire grate formed of a blank of sheet metal anddisposed in the cavity, the fire grate comprising: a lower elevationportion defining a perimeter edge; a higher elevation portion disposedsubstantially at the central axis, the fire grate shaped to form an arcshape between the lower elevation portion and the higher elevationportion; a plurality of radial stiffening ribs formed by bends in thesheet metal and extending in a direction between the lower elevationportion and the higher elevation portion; a plurality of ventilationholes through the sheet metal between the lower elevation portion andthe higher elevation portion.
 22. The fire pit of claim 21, wherein theperimeter edge of the fire grate is circular.
 23. The fire pit of claim21, wherein the fire grate is a spherical section with a radius ofcurvature larger than one-half of a width of the fire grate.
 24. Thefire pit of claim 21, wherein the fire grate further comprises adownward-facing lip around the perimeter.
 25. The fire pit of claim 21,wherein the plurality of radial stiffening ribs include first ribs of afirst length and second ribs of a second length different than the firstlength.
 26. The fire pit of claim 21, wherein a portion of the firegrate comprises an outer stiffening ring that includes no ventilationholes.
 27. The fire pit of claim 21, wherein the fire grate, theplurality of radial stiffening ribs, and the ventilation holes arearranged in a manner that they can be produced by stamping the sheetmetal.
 28. The fire pit of claim 21, wherein the fire grate isconfigured to support between 0 lb and about 190 lb of fuel attemperatures of between about −40° F. and about 1350° F.
 29. The firepit of claim 21, wherein the inner wall comprises an upward-facingsupport, the perimeter edge of the fire grate resting on theupward-facing support of the inner wall.
 30. A fire pit for burningsolid fuel to produce heat, comprising: an inner wall having a lowerportion and an upper portion; an outer wall having a lower portion andan upper portion; an air-filled space between the inner wall and theouter wall; a chimney formed by the inner wall and defining a centralaxis; a combustion area situated within the chimney; at least oneventilation hole within the upper portion of the inner wall; at leastone ventilation hole within the lower portion of the outer wall; a firegrate formed of from blank of sheet metal disposed within the combustionarea, comprising: an arc shape extending between a lower elevationportion defining a perimeter and a higher elevation portion disposedsubstantially at the central axis; at least one circumferentialstiffening ring extending at least partially about the higher elevationportion; and a plurality of ventilation holes through the sheet metalbetween the lower elevation portion and the higher elevation portion.31. The fire pit of claim 30, wherein the fire grate is supported onlyat the perimeter.
 32. The fire pit of claim 30, wherein the fire gratecomprises a plurality of radial stiffening ribs formed by bends in thesheet metal and extending in a direction between the lower elevationportion and the higher elevation portion.
 33. The fire pit of claim 32,wherein the plurality of radial stiffening ribs include first ribs of afirst length and second ribs of a second length different than the firstlength.
 34. The fire pit of claim 30, wherein the perimeter of the firegrate extends about the central axis and forms a complete circle. 35.The fire pit of claim 30, wherein the perimeter of the fire gratecomprises an outer rim terminating in a downward-facing edge around theperimeter, and wherein the inner wall comprises an upward-facingsupport, the downward facing edge of the perimeter edge resting on theupward facing support of the inner wall.
 36. A fire pit comprising: avertically extending outer wall comprising a plurality of airventilation holes; a vertically extending inner wall spaced from theouter wall to form an air gap therebetween, the inner wall comprising aplurality of air ventilation holes, the inner wall defining a cavity andhaving a central axis, the inner wall having a bottom end terminating inan upward facing support; a fire grate formed of a blank of sheet metaland disposed in the cavity, the fire grate comprising: a lower elevationportion defining a perimeter edge, the perimeter edge of the fire grateresting on the upward facing support of the inner wall; a higherelevation portion disposed substantially at the central axis, the firegrate shaped to form an arc between the lower elevation portion and thehigher elevation portion; and a plurality of ventilation holes throughthe sheet metal between the lower elevation portion and the higherelevation portion.
 37. The fire pit of claim 36, wherein the fire gratecomprises a plurality of radial stiffening ribs formed by bends in thesheet metal and extending in a direction between the lower elevationportion and the higher elevation portion.
 38. The fire pit of claim 37,wherein the plurality of radial stiffening ribs include first ribs of afirst length and second ribs of a second length different than the firstlength.
 39. The fire pit of claim 36, wherein the fire grate comprises aplurality of circumferential stiffening ribs formed by bends in thesheet metal and extending transverse to a direction between the lowerelevation portion and the higher elevation portion.
 40. The fire pit ofclaim 36, wherein the perimeter edge of the fire grate extends about thecentral axis and forms a complete circle.
 41. The fire pit of claim 36,wherein the perimeter edge of the fire grate comprises an outer rimterminating in a downward-facing edge around the perimeter, the downwardfacing edge of the perimeter edge resting on the upward facing supportof the inner wall.